High pressure waveguide window



p 19, 1961 J. E. TROUSDALE 3,001,160

HIGH PRESSURE WAVEGUIDE WINDOW Filed July 20, 1959 2 Sheets-Sheet 1 INVENTOR. (703W E. 70z/5 0045 Sept. 19, 1961 Filed July 20, 1959 J. E. TROUSDALE 3,001,160 HIGH PRESSURE WAVEGUIDE wmnow 2 Sheets-Sheet 2 I N V EN TOR. fay/v E. 7%005044/5 Wm AQZLWAM/ fiflhlfifi Patented Sept. 19, 1961 free 3,001,160 HIGH PRESSURE WAVEGUIDE WINDOW John E. Trousdale, Lem ngton, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed July 20, 1959, Ser. No. 828,424 8 Claims. (Cl. 333-98) This invention relates in general to pressurized waveguides and in particular to pressurizing waveguide Wmdows disposed within the guide.

The ambient operating conditions of temperature, humidity and pressure are often extreme for submarine and airborne radar. Operation under these rapidly changing conditions must be given serious consideration. When an aircraft descends quickly to an area of higher absolute humidity such as exists near ground level, frost and dew accumulate on both mechanical and electrical parts. Furthermore, sweating occurs in humid areas where substantial day to night temperature dilferentials exist. Aboard submarine similar conditions will prevail where the vessel surfaces from a cold subsurface to a hot humid atmosphere at sea level. This condensation or surface wetting will result in short circuits, arcing, corrosion, and ineificient transfer of high frequency energy through waveguides. Arcing in transmission lines may occur at connectors, rotary joints and other circuits where high differences of potentials may exist. Reduction or elimination of arcing is accomplished particularly by pressurization, even though the system can be hermetically sealed. It is common procedure to maintain pressurization by a pump since absolute or true hermetic scaling is diflicult, expensive and impracticable. The problem aboard submarines becomes even more severe since high external water pressures are encountered at great sea depths thereby necessitating sealing in the event the particular bulkhead involved becomes filled with water.

One object of the present invention is to provide a mechanically simple and eflicient waveguide window seal capable of withstanding high pressure and adaptable for use within the confines of a waveguide.

A further object is attaining a minimum of electrical discontinuity and attenuation when the window of this invention is introduced within the waveguide.

Another object is that the pressurizing window of this invention be detachably secured within the waveguide.

Other objects and advantages will be apparent from the following tion and the novel features thereof will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

FIG. 1 is a longitudinal sectional elevation plan of one embodiment developed in accordance with the present invention.

FIG. 2 is a similar sectional elevation but illustrating a modification of the invention.

FIG. 3 is a longitudinal sectional elevation plan of another embodiment of the invention.

In the embodiment of the invention illustrated in FIG. 1 the pressurizing waveguide window comprises two generally similar hollow metallic waveguide sections 1 and 2 disposed end to end with a pressurizing plug 3 disposed within the continuous passage thusly formed. The hollow guide sections 1 and 2 are generally similar except that different external mounting flanges 4 and 5 are illustrated for each one though these sections may be identical. The sections shown are of equal length though not necessarily so, and are disposed in an end to end relationship coupled together by any suitable means, prefdescription of embodiments of the inven erably as here, by bolts 6 extending through a lateral flange 7 of one section and secured by internal mating threads within the flange 8 of the opposing section. Both flanges 7 and 8 may be identical, but where mounting to a bull or plate is desired one flange 7 may be constructed somewhat shorter transversely of the sections than the facing flange 8 allowing bolts 9 passing through flange 8 to be secured to the bull or plate. These bolts 9, as screws 6, are symmetrically disposed around the flanges in order to insure constant pressure between the mating surfaces. Two endless grooves 10 and 11 are located in the mating surfaces of the flanges 7 and 8 and extend peripherally of the sections. Elastic rubber-like 0 rings 12 and 13 are disposed within each of the grooves 10 and 11 under substantial compression between the bottom of each groove and its mating surface when the flanges are coupled together, forming a seal against radial or outward fluid leakage.

The guide passage 14 of each section is circular in transverse cross section at the coupled ends (line a) of the sections and from this junction the passage in each section first gradually tapers slightly in a direction away from the junction and remaining symmetrical about the guide passage axis 15. Over a second portion it continues to taper except at a steeper rate. The first such taper is defined for that guide passage wall lying between lines a and b, While the latter portion lies between lines b and c. The passage thereon forms a transition between the circular section at line c and rectangular cross-section at the end opposite the junction, line d. It should be noted that the cross-section dimensions of the waveguide passage described above may be determined by reference to any well-known treatises on waveguide theory and that the preferred length of the transition portion of the passage measured from the line c, to the opposite end, line d be approximately a quarter wavelength at the geometric mean wavelength of the required bypass frequency.

A plug 3 of electrically insulating material, whose surface is complementary to that portion of the guide passage wall which is defined by the lines a and b on either side of the coupled junction, is disposed symmetrically with respect to the junction and within the guide passage substantially filling it for that portion, throughout which its surface is thusly complementary. The plug surface from the lines I) to c may be complementary to the guide passage wall therein or as illustrated, it may gradually taper in a direction away from the passage wall being only slightly distant therefrom at line c.

The plug 3 is provided with a peripheral groove 16 intermediate between that portion of the plug defined by lines b and c and preferably disposed on that side of the plug facing the area of higher pressure. From line 0, the free ends of the plug taper in directions out- Wardly from the junction of the coupled flanges and symmetrically about the guide axis 15. Since the guide passage, in a transverse direction is dimensionally greater at its center line a) than at line 11, its peripheral wall therein forms a tapered abutment having shallow facing shoulders 17 thereby confining the plug against lengthwise movement when the guide sections are coupled together. An endless elastic sealing member 18, as for instance, an elastic rubber-like O ring, is disposed within the groove 16 under substantial radial compression between the bottom of the groove and the adjacent guide passage wall when the flanges are coupled together forming a seal preventing fluid movement past the plug along the passage.

In order to facilitate efficient transfer of electromagnetic energy through the guide passage with a minimum of attenuation, the plug can be constructed of any number of materials, some already successfully used for this purpose including polystyrene and polytetrafiuoroethylcne, the latter being widely marketed in the trade under the name of Teflon by the E. I. du Pont de Nemours Co. Further, the length of the guide passage from line to line a, comprising each circular to rectangular transition, should be approximately a quarter wavelength long at the geometric mean wavelength of the required bypass frequency and the entire circular portion of the guide passage should be approximately twice this length namely, one-half wavelength long. The plug should be of a length such that when it is symmetrically disposed within the coupled sections 1 and 2, the passage length will be equal to the plug length.

An alternate embodiment of this invention is illustrated in FIG. 2 wherein the pressurizing window comprises a metallic window member having a plate-like portion 21 with a window 22 (rectangular passage) therethrough and a metallic flange 23 extending perpendicularly therefrom. The rectangular passage 24 of the flange portion is larger in cross section than the window 22 and in alignment with the window. A flange member 25 having a rectangular passage 26 therethrough from face to face, abuts the free end of the flange portion 23 and has its passage aligned with and dimensionally equal to the window of member 20 so that an enlarged recess 24- for confining a plug 27, is formed by the inner peripheral wall of the flange 23 and the peripheral flanges 28 which overlap the flange passage 26 and form inwardly facing abutments '29.

A plug 27 of electrically insulating material, whose peripheral surface is complementary to the recess passage wall of the flange and to the abutments 29 at its ends and substantially fills that portion of passage, is disposed therein. The shoulder abutments 29 confine the plug within the passage 26 against lengthwise movement when the flange member 21") abuts the free end of flange 23 and is coupled to it by suitable means such as screws 39. The plug is provided with a peripheral groove 31 intermediate between its ends. An endless elastic sealing element 32, as for instance an elastic rubber 0 ring, is disposed within the groove 31 under substantial radial compression between the bottom of the groove and the adjacent abutting passage wall when the flange member 25 and the flange 23 are coupled together forming a seal preventing fluid movement past the plug along the passage. Screws 33, such as illustrated, may be employed to couple the pressurizing window to suitable internally rectangular waveguides (not shown) at the flange member 25 and the plate-like portion 21 with their respective passages aligned.

The plug may be fabricated of materials previously described for the tapered plug of the first described embodiment and should be of a length determined by the following equation:

2g=plug length along the flange passage 2a=mean value wavelength of the required bandpass frequency 2c=cutoff wavelength of the cavity section e=dielectric constant of the plug material where 4 when the flanges abut and are coupled by screws to the window member their passages are in alignment and abutments 46 are formed bythe inner faces of the flanges i1 that overlap the passage through the window member 43.

A plug 47 similar both dimensionally and in material composition to the plug of the second described embodiment is disposed within the window member passage and confined therein by the abutments 4s and substantially fills this passage. A peripheral groove 48 and an elastic sealing element 49 disposed therein similar to that encountered in the second described embodiment, form a seal preventing fluid movement past the plug along the passage when the flanges 41 abut and are coupled to the window member 43.

It will be understood that various other changes in the details, materials and arrangement of parts which have been herein disclosed in order to disclose the nature of this invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. A waveguide window construction resisting fluid leakage along a portion of it between sections thereof that may be subjected to a fluid pressure diflerential between such sections, which comprises hollow waveguide sections disposed in end to end relationship and coupled together to form a continuous guide passage, a plug of electrically insulating material disposed across and substantially filling said passage adjacent the coupled sections and confined therein by said coupled sections against movement along the sections, said plug having a pcripherally extending channel, an endless elastic sealing member disposed in said channel under substantial compression between the bottom of said channel and the passage wall and forming a seal preventing passage of fluid along the passage past said plug.

2. A waveguide window construction as set forth in claim 1, wherein said plug is symmetrically disposed within said continuous guide passage and of a length approximately equal to the wavelength of the high frequency energy to be transmitted therethrough with its free ends tapered.

3. A waveguide window construction as set forth in claim 2, wherein the passage of said hollow Waveguide section is circular in transverse crosssection for a portion of the section extending for a distance in a direction away from the coupled end, and having its greatest cross-sectional area at the coupled end, the remaining portion of said passage forming a smooth continuous transition from said circular cross-section to a rectangular cross-section at the free end of the waveguide section, said plug disposed across and substantially filling that portion of the passage being circular in transverse crosssection with its free ends tapered and extending to the said free end of the waveguide section.

4. A waveguide window construction as set forth in claim 3, wherein each of said hollow waveguide sections has a laterally extending flange disposed at the communicating end of said section, said flanges tightly abutting face to face when said hollow waveguide sections are in communication, means for tightly coupling said flanges, one of said flanges having an endless peripheral channel on its abutting face, an endless elastic sealing member disposed in said flange channel under substantial compression between the bottom of said flange channel and the facing surface of the abutting flan e on the opposing hollow waveguide section.

5. A waveguide window construction as set forth in claim 1, wherein said hollow waveguide section passage is transversely enlarged adjacent the coupled junction which confines said plug between the abutments of the passage wall against lengthwise movement.

6. A waveguide window construction as set forth in 5 claim 5, wherein said continuous guide passage is rectangular in transverse cross-section and said plug forming a wall across said guide passage in said enlarged portion.

7. A waveguide window construction as set forth in claim 6, wherein said plug and said enlarged portion have a longitudinal dimension equal to one-half the wavelength of the transmitted high frequency energy.

8. A waveguide construction to provide fluid leakproof seals between two portions having different internal fluid pressures, comprising two metallic members each having a guide passage therethrough and disposed end to end with their passages at the abutting ends communicating to form a conducting channel, said channel being somewhat enlarged cross-sectionally adjoining the passage junction, means to confine the ends of said members in an abutting relationship, an electrically insulating plug disan electrically insulating fluid sealing elastic element disposed within said groove under substantial radial compression between the bottom of said groove and the wall defining said channel passage, and forming a seal preventing fluid movement past said plug along said passage.

References Cited in the file of this patent UNITED STATES PATENTS 2,922,970 Reed Jan. 26, 1960 FOREIGN PATENTS 775,315 Great Britain May 22, 1957 

